A critical analysis of the direct effects of dredging on fish

Dredging can have significant impacts on aquatic environments, but the direct effects on fish have not been critically evaluated. Here, a meta‐analysis following a conservative approach is used to understand how dredging‐related stressors, including suspended sediment, contaminated sediment, hydraulic entrainment and underwater noise, directly influence the effect size and the response elicited in fish across all aquatic ecosystems and all life‐history stages. This is followed by an in‐depth review summarizing the effects of each dredging‐related stressor on fish. Across all dredging‐related stressors, studies that reported fish mortality had significantly higher effect sizes than those that describe physiological responses, although indicators of dredge impacts should endeavour to detect effects before excessive mortality occurs. Studies examining the effects of contaminated sediment also had significantly higher effect sizes than studies on clean sediment alone or noise, suggesting additive or synergistic impacts from dredging‐related stressors. The early life stages such as eggs and larvae were most likely to suffer lethal impacts, while behavioural effects were more likely to occur in adult catadromous fishes. Both suspended sediment concentration and duration of exposure greatly influenced the type of fish response observed, with both higher concentrations and longer exposure durations associated with fish mortality. The review highlights the need for in situ studies on the effects of dredging on fish which consider the interactive effects of multiple dredging‐related stressors and their impact on sensitive species of ecological and fisheries value. This information will improve the management of dredging projects and ultimately minimize their impacts on fish.     

Longitudinal variations in exposed riverine sediments: a context for the ecology of the Fiume Tagliamento,Italy

1. A key component of physical habitat along braided river systems is the exposed riverine sediment within the active zone. The relatively unmanaged, gravel‐bed Fiume Tagliamento, Italy, provides the focus for exploring two ecologically important properties of exposed riverine sediments: their within‐patch and between‐patch variability in calibre. 2. To characterize between‐patch variation in exposed riverine sediments, replicate (within‐patch) samples were obtained from three geomorphologically distinct locations along 130 km of the river: bar heads along the margin of the low‐flow channel, the heads of major bars across the exposed surface of the active zone, and floodplain surfaces. A photographic technique enabled rapid and consistent field sampling of the coarse sediments at bar heads along the low‐flow channel margin and on major bars across the dry bed. 3. A downstream decrease in particle size and an increase in within‐patch heterogeneity in sediment size were observed within bar head sediments along the margin of the low‐flow channel. Comparisons between major bar and low‐flow channel samples revealed greatest within‐patch variability in individual sediment size indices (D₅₀, A‐ and B‐axes of the larger particles) at headwater sites, greatest between‐patch variability in the three measured indices in the central reaches, and lowest between‐patch variability at downstream sites. However, there was a distinct increase in the overall heterogeneity in particle size, which was sustained across all patches, in a downstream direction. 4. There was a clear downstream decrease in the size of floodplain sediments in the headwaters, but thereafter there was no distinct downstream trend in any of the calculated particle size indices. 5. The geomorphological controls on the observed patterns and the potential ecological significance of the patterns, particularly for plant establishment, are discussed in relation to the relative relief of the active zone, and the highly variable hydrological and climatic regime along the river. Copyright © 2000 John Wiley & Sons, Ltd.     

Harvesting an invasive bivalve in a large natural lake: species recovery and impacts on native benthic macroinvertebrate community structure in Lake Tahoe,USA

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Use of tissue and sediment‐based threshold concentrations of polychlorinated biphenyls (PCBs) to protect juvenile salmonids listed under the US Endangered Species Act

• 1. Under the Endangered Species Act, the National Marine Fisheries Service has authority to protect listed species from any adverse actions that may jeopardize the population's ability to recover and increase to sustainable levels. Listed salmon species in the northwest United States are known to travel through urban areas in their migration from river to ocean. Species such as the chinook salmon (Oncorhynchus tshawytscha) often spend several weeks in these urban estuaries where they can be highly exposed to urban‐related contaminants that reside in the sediments and accumulate in their prey species. The concern is that these contaminants are bioaccumulated to levels that may impact the ability of individual salmon to grow and mature normally. This paper provides a framework for determining the tissue and sediment concentrations of polychlorinated biphenyls (PCBs) that are likely protective against adverse effects in listed salmonid species.
• 2. The relevant ecotoxicological literature was examined and 15 studies were selected that met the pre‐established criteria outlined here. For each study, the lowest tissue concentration (residue) of total PCBs associated with a biological response was selected. The tissue concentration associated with the 10th percentile of these 15 studies was chosen to represent the residue effect threshold (RET) above which wild juvenile salmonids would be expected to exhibit adverse sublethal effects from accumulated PCBs. This value (2.4 μg PCBs g^?1 lipid) is expressed in terms of the lipid‐normalized concentration because of the large effect lipid can have on the expressed toxicity and the substantial variability in lipid content observed in salmonids over their life cycle.
• 3. A sediment concentration that is expected to produce the RET was then determined using the biota‐sediment accumulation factor approach. The sediment effect threshold, which varies with the total organic carbon content in sediment, is the level above which adverse effects may be expected in juvenile salmonids due to accumulation of PCBs from environmental exposure. Bioaccumulation of PCBs was examined in one river system as a model for determining an appropriate bioaccumulation factor for wild juvenile chinook salmon.
• 4. Evaluation of exposure to potentially deleterious concentrations of PCBs based on tissue residues is the preferred approach; however, the sediment effect threshold may also be used in cases where bioaccumulation has been characterized in an estuary. The threshold values presented here are intended as interim guidelines that should be modified as more data become available. Additionally, because of the uncertainty around many of the factors and assumptions that comprise the single threshold effect values, it is recommended that future studies be employed to help determine a range of acceptable values that would afford protection under various environmental and biological conditions.

Published in 2002 by John Wiley & Sons, Ltd.     

Effect of sediment on growth and survival of post-larval Litopenaeus stylirostris (Boone, 1931)

The sediments from four areas that are used or will be used for shrimp culture were evaluated for their effect on post‐larvae growth of Litopenaeus stylirostris. Texture, organic matter, total, and bio‐available fraction of phosphorus, manganese, iron, zinc, copper, and cadmium of the sediments were measured. A positive significant correlation was obtained between total and bio‐available concentrations of iron, cadmium, and manganese, but not for copper, phosphorus, or zinc. Significant differences in final weight, survival rates, and shrimp yield were obtained among treatments. The highest survival rates were obtained with sediments that had the highest manganese levels. This survival high rate was significantly correlated with total manganese content of the sediment (r=0.92). The highest final weight were obtained in treatments with sediments containing higher levels of phosphorus, which was reinforced by a significant positive correlation between final weight and total and bio‐available phosphorus (r=0.94 and 0.95 respectively), while final weight seems adversely affected by high concentrations of copper (r=?0.83) in the sediment. Texture of the sediment influenced shrimp yield, with lower values for sandy sediments relative to silty sediments.     

滆湖北部底泥疏浚的生态效应研究

为研究滆湖北部湖区生态系统对底泥生态疏浚的动态响应,2012年10月~2013年9月在滆湖北部湖区采集沉积物和生物样品,分析底泥疏浚对底泥营养盐含量、浮游植物、底栖动物和大型水生植物群落结构的影响。结果表明,滆湖北部疏浚区的总氮、总磷和有机质营养盐含量低于未疏浚区,说明底泥疏浚是削减沉积物内源负荷的有效手段。与未疏浚区相比,疏浚区浮游植物的密度、生物量有所减少,且群落中蓝藻所占的比例下降,浮游植物多样性指数上升,一定程度上减少了滆湖北部发生蓝藻水华的风险。疏浚区底栖动物中的寡毛类的数量和生物量与未疏浚区基本相等,而摇蚊类和软体动物的密度和生物量则下降了80%以上。底泥疏浚区大型水生植物的种类、覆盖度和生物量与未疏浚区相当。     

High β‐diversity maintains regional diversity in Brazilian tropical coastal stream fish assemblages

Understanding spatial patterns of species diversity and the variables that structure biological communities is critical to successful ecosystem management. Regional diversity (γ) can be considered a combination of local diversity (α) and among sites variation (β). Using abundance data of fish species in 19 stream stretches, an analysis of diversity partitioning was used to determine the contribution of α‐ and β‐diversity to γ‐diversity. Redundancy analysis was applied to find the contribution of environmental variables and spatial configuration to species composition. Intersite variation contributed significantly to γ‐diversity. Spatial configuration and instream heterogeneity (coarse substrate, channel width, water velocity and shading) and riparian vegetation were related to local fish abundances. Conservation actions should consider that all streams are important, and prioritisation of just a small number of the richest sites is not appropriate.     

Effects of increasing concentrations of fine suspended sediment on the survival,growth, condition factor and gill condition of artificially reared juveniles of Oncorhynchus masou,Salvelinus leucomaenis and Plecoglossus altivelis

Little is known about the effect of chronic turbidity created by fine suspended sediment on the health and growth of artificially reared Oncorhynchus masou, Salvelinus leucomaenis and Plecoglossus altivelis—three important aquaculture species in Japan. This study compared survival rate, daily growth rate, condition factor (estimated from the ratio of standard length to weight) and gill condition among like‐sized juveniles exposed to fine suspended sediment (<2‐µm fraction) at concentrations of 0, 50, 100 and 500 mg/L, after 21 days. Even at 500 mg/L, there was almost no damage to the gill condition in all species. In O. masou, the daily growth rate was unexpectedly high in the 500‐mg/L treatment group, and condition factor was higher at sediment concentrations of 100 and 500 mg/L than at 0 mg/L. In S. leucomaenis, daily growth rate was significantly lower in the 500‐mg/L treatment group as compared with all other groups, but condition factor did not significantly differ among the treatments. The survival rates of O. masou and S. leucomaenis did not significantly differ among the treatment groups. In P. altivelis, neither survival rate, daily growth rate nor condition factor significantly differed among the treatments. The concentration of fine suspended sediment that affects the growth and condition factor of each of these species is likely related to their natural habitat.     

Effects of Hydraulic Dredging for Mercenaria mercenaria,Northern Quahog,on Sediment Biogeochemistry

A before‐after‐control‐impact (BACI) experiment was conducted to examine the effects of hydraulic clam dredging on sediment biogeochemistry of a leased shellfish bed of Mercenaria mercenaria, northern quahog, over the course of an entire growing season. Six study plots (0.67 ha each), three dredged and three not dredged, off of Milford, Connecticut, in Long Island Sound, were sampled from May to October 2009 for porewater fluxes of total ammonia, oxygen, and hydrogen. Particulate samples were also analyzed for grain size, total nitrogen, total carbon, total sulfur, and organic carbon. Statistical analysis indicated no significant difference between dredged and not dredged sites. Grain size and oxygen flux explained 22% of the variation in the total benthic species assemblages; grain size and either total carbon or organic nitrogen explained 18% of the variation in molluscan abundance. Our study demonstrates that one‐time hydraulic shellfish harvesting had minor effects on the sediment chemistry of a leased clam bed.     

Testing the potential for improving quality of sediments impacted by mussel farms using bioturbating polychaete worms

Biodeposits from farmed mussels severely influence the biogeochemistry of sediments by increasing the levels of organic matter (OM). Mitigation of such negative impacts is important for the development of sustainable aquaculture operations. As a step towards developing methods for remediation of coastal sediments affected by mussel farming, the effects of the polychaete, Hediste diversicolor was evaluated experimentally. In a series of field‐ and laboratory experiments we tested hypotheses about the effects of polychaetes on sediment oxygen consumption, nutrient fluxes and sulphide pools under different polychaete densities and sedimentation regimes. The experimental results support the idea that polychaetes can mitigate negative effects on the benthic environment beneath mussel farms. H. diversicolor oxidized the sediment and generally enhanced the oxygen consumption, and thus the decomposition of OM. The accumulation of pore water sulphides were reduced and fluxes of nutrients across the sediment‐water interface increased. Additional calculations suggest that the effects of polychaetes were mainly indirect and driven by increased microbial activity due to the borrowing activity of the polychaetes. Trends of increasing decomposition with increasing polychaete density suggest that the decomposition could be further enhanced by higher densities. Overall, we concluded that H. diversicolor is a potentially strong candidate for remediation of mussel farm sediments. The results show that sediments inhabited by H. diversicolor have high assimilative capacity of OM and oxygen conditions are significantly improved following the addition of polychaetes at naturally occurring densities. However, technological developments are needed in order to allow the approach to be used in practice.     

The role of coarse woody debris in forest aquatic habitats: Implications for management

• 1 Throughout the Temperate Forest biogeographical zone, river valleys were once heavily wooded. Fallen trees had a major impact upon river systems by ponding water and storing sediments, and valley floors were characterized by extensive wetlands with networks of minor channels linking to the main channel. Concern for environmental conservation and for the rehabilitation of damaged aquatic ecosystems has led to research on the links between river channel dynamics and vegetation, and an interest in the use of dead wood for environmentally sensitive engineering approaches to river management.
• 2 Accumulations of coarse woody debris (CWD) have an impact on the hydrological, hydraulic, sedimentological, morphological and biological characteristics of river channels. These impacts are very significant for the stability and biological productivity of river channels in forested catchments.
• 3 As a result of the geomorphological and ecological importance of CWD in river channels in forested catchments, such debris requires careful management. In particular indiscriminate removal of CWD should be avoided.
• 4 In the context of commercial forestry, a sequence of linked management options can be employed to control sediment and organic matter transport within river systems and to enhance channel stability and physical habitat diversity. These management options include selective removal of less stable debris, addition of debris to the river where the natural supply is inadequate, the maintenance of buffer strips of riparian trees which can act as a source of CWD, and the active management of woodland buffer strips to provide a wide range of physical habitat characteristics including light, temperature, flow, sediment transport and substrate conditions, thereby promoting high biological diversity within the river environment.

     

Fractionation of phosphate in marine aquaculture sediments: optimization of the ethylenediaminetetraacetic acid method and comparison with other procedures

The ethylenediaminetetraacetic acid (EDTA) method was compared with two other P‐fractionation methods, Sedex and Hieltjes & Lijklema (H. & L.), in order to choose a suitable method that extracts better the inorganic (inorg‐P) and organic (org‐P) phosphate from marine aquaculture sediments. The EDTA method gave reliable results and did not change the P‐composition of the sediments during the analysis. The Sedex method can be improved if the quantity of pre‐extracted org‐P is separately determined after digestion, and the org‐P can thereby corrected. The Sedex method underestimates the org‐P present in the sediments (?59%), whereas the calcium‐bound phosphate (CaCO₃≈P) is overestimated (+17%) in comparison with the EDTA method. The NaOH and HCl used in H. & L. method are not specific to extract inorg‐P from the sediments. To provide optimal extractions of inorg‐P in muddy sediments containing 1% org‐C and 15% CaCO₃, the EDTA method was optimized according to extraction times, dithionite concentration and solute/solid ratio. Five extractions of 2‐h duration each with Ca‐EDTA are required to extract more than 95% of the iron‐bound phosphate (Fe(OOH)≈P) while the extraction of CaCO₃≈P with Na‐EDTA takes more than 96 h. The concentration of dithionite up to 1% did not influence the amount of P and Fe extracted (P=0.098 and 0.174 respectively), whereas a solute/solid ratio of 40:1 was best suitable for the optimal extraction of Fe(OOH)≈P. These conditions can be applied to analyse P composition of other marine pond sediments having similar texture and chemical composition.     

Redeveloped docks as artificial lagoons: The development of brackish-water communities and potential for conservation of lagoonal species

• 1 The use of redeveloped docks for the conservation of lagoonal communities is considered with particular reference to the South Docks in Liverpool.
• 2 Redevelopment of the previously derelict South Docks since 1981 has created a semi-enclosed, brackish body of water by dredging of dock basins that were filled with silt. The development of biological communities on the walls and in the sediments of these docks has been studied.
• 3 A reasonably diverse flora and fauna was established on the walls within approximately six years, but a persistent sediment-dwelling community has not yet developed.
• 4 Over 90 species of macroflora and macrofauna have been recorded from the South Docks to date. Three of these species are considered to be lagoonal specialists.
• 5 Considerations for the management of docks as a resource in the conservation of lagoonal communities are discussed.

     

Associations between stream hydrogeomorphology and co‐dependent mussel–fish assemblages: evidence from an Ohio,USA river system

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Blue sucker stock characteristics in the upper Yazoo River basin, Mississippi, USA

Blue sucker Cycleptus elongatus (L.) in the upper Yazoo River basin, Mississippi, USA was studied using overnight hoop net sets (n = 4093) during 1988 and 1990–1998 to determine the influence of channel dredging. There were 264 blue suckers captured, ranging from 3 to 11 years of age. Length ranged from 265 to 700 mm and weight from 120 to 4700 g. Concurrent studies with smaller mesh hoop nets failed to capture any juvenile blue suckers. Catch‐per‐unit‐effort (CPUE: fish net^?1) declined throughout the study in the Yalobusha River, a river subjected to channel dredging during 1988 and 1994. With the exception of limited hydraulic dredging in the Tallahatchie River, there was no dredging in the other Yazoo River tributaries, nor were there declines in blue sucker catch rates in these rivers. Throughout the upper Yazoo River basin, blue sucker stocks were dominated by adult fish, and there was little evidence of reproduction or recruitment. Conservation of the blue sucker in the upper Yazoo River basin should include actions that ensure the functional integrity of this floodplain river ecosystem and elimination of channel dredging throughout the basin.     

River bed features affect the riverine distribution of two amphidromous Rhinogobius species

Tamada K. River bed features affect the riverine distribution of two amphidromous Rhinogobius species.
Ecology of Freshwater Fish 2011: 20: 23–32. © 2010 John Wiley & Sons A/S Abstract – Nest‐use patterns of two amphidromous gobies, Rhinogobius sp. LD (large dark type) and CB (cross‐band type), were studied along the course of the Aizu River, Japan. Males of both species build and defend nests under stones. Adult distributions of the two gobies do not overlap in this river. LD is more predominant in the upper reaches than CB. The stone size on the river bed in the region inhabited by LD was larger than that in the region inhabited by CB. LD was found to have larger body size, larger nest stones, egg clusters and egg numbers than CB. Laboratory nest choice experiments showed that LD selects larger nests than CB. This trend can be explained by a size‐assortative nest preference across these species. The longitudinal distribution of stone size seems to affect upstream migration and reproduction of these species.     

Effects of stocking density on intermediate culture of the razor clam Ensis arcuatus (Pharidae: Bivalvia)

Commercial production of most bivalve species involves a phase of intermediate cultivation during which juveniles are grown under protected conditions until they can be transferred to the final grow‐out location. Consequently, the aim of this study was investigating the effect of density on growth and survival in the intermediate culture of the razor clam Ensis arcuatus in raft. Two series of experiments were performed, using in the first experiment two holding systems: 5‐L plastic bottles and PVC cylinders, both perforated, covered with a 1 mm mesh net to prevent razor clam escape and a 10‐cm layer of coarse grained sand (300–1200 μm grain diameter). In this trial, two stocking densities were tested: 0.15 and 0.30 kg m^?2. In the second one‐two densities were essayed (0.62 and 1.24 kg m^?2) in the PCV cylinders. In the first experiment after 27 of trial higher growth in cylinders at low density was observed. At the end of this trial all juveniles died in the 5‐L plastic bottles and higher growth and survival were recorded in the cylinders at low density. In the second experiment, significant differences in growth and survival were found on day 70, with the best results at low density. Five‐L plastic bottles must be rejected as holding system for the intermediate culture of E. arcuatus and the PVC cylinders at low densities could be a good alternative. At the end of the experiment razor clams reached the adequate size for their transfer into the grow‐out system.     

The effects of stream substratum composition on the emergence of salmonid fry

Sternecker K, Geist J. The effects of stream substratum composition on the emergence of salmonid fry.
Ecology of Freshwater Fish 2010: 19: 537–544. © 2010 John Wiley & Sons A/S Abstract – Salmonid fishes are target species for the conservation of freshwater habitats, but their natural reproduction is often insufficient. The emergence of fry is a crucial phase in the life cycle of salmonids and the stream substratum is the key habitat which regulates the emergence success. In this study, brown trout (Salmo trutta) and Danube salmon (Hucho hucho) eggs were exposed to different sediment textures and the emergence and the postemergence survival and growth were observed under constant water chemical conditions in the laboratory. In both species, textural effects on emergence rate, chronology of emergence, survival rate after emergence and growth after emergence were detected. Fine‐textured substratum (5–8 mm) formed a physical barrier to the posthatch migration of salmonids from the interstitial zone to the open water. The time period between the first and the last emerged fish was shorter in treatments with fine texture compared with coarse substratum. The survival rate was higher in treatments of coarser sediment. The effects of different textures on the growth of fry after emergence differed between brown trout and Danube salmon, which can be explained by different life history strategies. These results suggest that physical characteristics of substratum texture can have strong effects on salmonid emergence, and ultimately on the persistence of salmonid populations. They also suggest that biodiversity conservation in stream ecosystems can greatly benefit from an inclusion of the physical characteristics of the stream bed into catchment‐based management plans.     

Effects of sedimentation on an endangered benthic fish,Cobitis shikokuensis: is sediment‐free habitat a requirement or a preference?

A negative correlation between the degree of fine sediment deposition and the abundance of stream benthic fishes has often been reported, although the causal mechanisms for this effect are not fully understood. To better understand the influence of sedimentation, it is important to clarify whether it alters the habitat required by fish, or merely preferred by them. We conducted two enclosure experiments in the field to examine (i) whether an endangered benthic fish, Cobitis shikokuensis, prefers sediment‐free substrate and (ii) whether fine sediment deposition has negative effects on the physiological condition of C. shikokuensis. The first experiment, which used three types of substrates, ‘cobble’, ‘pebble’ and ‘mixture of fine sediment and pebbles’, showed that C. shikokuensis avoided the mixture. The second experiment, which compared the physiological condition of fish reared in enclosures with either a pebble or mixture substrate, showed that the condition of the fish in the latter group declined more quickly. These results suggest that, for C. shikokuensis, sediment‐free substrate is a habitat requirement, not merely a preference, and that excessive input of fine sediment due to human activities can cause a decline in the population of this species.